U.S. Pat. No. 3,342,474 issued to K. Bittel on Sept. 19, 1967 discloses a liquid spring having a body of compressible liquid trapped within a piston-cylinder assembly. Such a spring is attractive for vehicle suspension because a relatively small quantity of compressible liquid is able to absorb large amounts of energy. A suitably designed suspension using a liquid spring can provide relatively high road wheel travel on the order of 18 inches.
One problem when using liquid springs is the thermal expansion due to ambient temperature variations and damping heat generated by road wheel travel. The present invention suggests a compensator valve which vents excess liquid to a pressurized accumulator when the road arm approaches the full rebound position. The accumulator pressure determines the rebound pressure setting of the liquid spring.
The present invention also suggests a damper for the liquid spring, comprising a damper piston and a two-way passage means from one face of the damper piston to the other face. During movement of the road wheel in the jounce direction the damper liquid flow rate is restricted to thereby control road wheel acceleration. When the wheel is pushed upward toward the vehicle the damping is controlled by an acceleration sensing bypass valve which can cause the damping to be eliminated when the wheel is impacted suddenly. When the vehicle is moving downward with the wheel moving only in the horizontal direction the acceleration sensing bypass valve cannot eliminate the damping. Thus damping force is not applied to the vehicle upon sharp impacts of the wheel and the vehicle motion is still damped after hitting a bump. During rebound movement the damper liquid flow is relatively unthrottled to permit rapid wheel travel, and to maintain the suspension effect.